Is there any incidence or statement in the scriptures which shows that varna/caste was not deduced from birth/parentage, and was deduced only from "qualities independent of parentage"(without referring to parentage at all).
The top answer to this question uses this verse as a reference:
catur-varnyam maya srstam
guna-karma-vibhagasah - (BG 4.13)
and says that "They substituted heredity in place of qualities", but doesn't provide any reference to a prior system which didn't consider heredity. All authentic commentaries interpret the word "guna" here to mean that "qualities acquired by birth". So, this verse doesn't seem to fulfill my need.
Also, please note that I'm not asking about the flexibility of varna system.
Please cite direct scriptural references(if possible with links).
Edit: It would do if Shruti(Vedic or Upanishadic) references are provided which show that varna/caste was deduced from birth/parentage, and was not deduced from "qualities independent of parentage".